Hi, On Thu, Jul 21, 2011 at 10:34:35AM +0200, Richard Guenther wrote: > On Wed, 20 Jul 2011, Ulrich Weigand wrote: > > > Richard Guenther wrote: > > > On Tue, Jul 19, 2011 at 8:20 PM, Ulrich Weigand <uweig...@de.ibm.com> > > > wrote: > > > > The problem is that in this expression > > > > disappear = VIEW_CONVERT_EXPR<struct VecClass>(x_8); > > > > the rhs is considered unaligned and blocks the SRA transformation. > > > > > > > > The check you added for SSA_NAMEs doesn't hit, because the SSA_NAME is > > > > encapsulated in a VIEW_CONVERT_EXPR. When get_object_alignment is > > > > called, > > > > the VIEW_CONVERT_EXPR is stripped off by get_inner_reference and the > > > > SSA_NAME appears, but then get_object_alignment doesn't handle it > > > > and just returns the default alignment of 8 bits. > > > > > > > > Maybe get_object_alignment should itself handle SSA_NAMEs? > > > > > > But what should it return for a rvalue? There is no "alignment" here. > > > I think SRA should avoid asking for rvalues. > > > > I must admit I do not fully understand what the SRA code is attempting > > to achieve here ... Could you elaborate on what you mean by "avoid > > asking for rvalues"? Should the SRA code never check the RHS of an > > assignment for alignment, only the LHS? Or should it classify the RHS > > tree according to whether the access is rvalue or lvalue (how would > > that work?)? > > Well, it should only ask for stores / loads. I'm not sure what we'd > want to return as alignment for an rvalue - MAX_ALIGNMENT? What should > we return for get_object_alignment of an INTEGER_CST for example? >
Yeah, we certainly should not be examining alingment of invariants and of conversions of ssa names in. As far as rvalues in general are concerned, I don't really know which gimple predicate that would be. A comment suggests is_gimple_val but that does not return true for a VIEW_CONVERT_EXPR of an SSA_NAME and would return true for aggregate variables (which perhaps would not be a problem, however they do have an alignment). So at the moment I'd go for stripping all conversions from exp before the first if in tree_non_mode_aligned_mem_p and adding is_gimple_min_invariant to the condition. Does that make sense? (I'm quite puzzled why non-gimple_reg vectors and complex numbers are not is_gimple_val while aggregate variables are and how that can be useful but that is unrelated.) Thanks, Martin
